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How much water should you drink

Explore an illustrative fluid calculation and compare it with general guidance. The formula does not establish a personal requirement; its assumptions and limits are explained below.

What the calculator actually does

This tool uses an illustrative rule: weight × 30 ml, then adds 350 ml per 30 minutes of activity and 400 ml when hot conditions are selected. These additions show how a planning estimate changes; they are not a validated way to establish your personal requirement. Exercise intensity, humidity, food and health conditions are not modelled.

General guidance and changing conditions

The NHS gives 6–8 cups or glasses of drinks per day as general guidance. Glass size matters, so this is not a fixed litre requirement. Prolonged activity, heat, illness, pregnancy or breastfeeding may change fluid needs. Tea, coffee, milk and other drinks count; some water also comes from food.

How to use the result

Compare your usual drinks throughout the day with general guidance and consider whether your circumstances have changed. The calculation does not require you to force down a missing amount. Thirst and pale-yellow urine can be everyday clues, but they do not replace assessment of symptoms or illness.

When you need another approach

If you have a prescribed fluid restriction or a heart or kidney condition, follow your individual care plan. This tool does not account for medicines and is not intended for children. Avoid drinking a large amount quickly simply to meet a displayed target: a model number is not an obligation.

NHS: drinks, hydration and changing fluid needs

This calculator is for information only and does not replace medical advice.